This invention relates generally to refrigerators and, more particularly, to a method and apparatus for controlling refrigeration defrost cycles.
Known frost free refrigerators include a refrigeration defrost system to limit frost buildup on evaporator coils. Conventionally, an electromechanical timer is used to energize a defrost heater after a pre-determined run time of the refrigerator compressor to melt frost buildup on the evaporator coils. To prevent overheating of the freezer compartment during defrost operations when the heater is energized, in at least one type of defrost system the compartment is pre-chilled. After defrost, the compressor is typically run for a predetermined time to lower the evaporator temperature and prevent food spoilage in the refrigerator and/or fresh food compartments of a refrigeration appliance.
Such timer-based defrost systems, however are not as energy efficient as desired. For instance, they tend to operate regardless of whether ice or frost is initially present, and they often pre-chill the freezer compartment regardless of initial compartment temperature. In addition, the defrost heater is typically energized without temperature regulation in the freezer compartment, and the compressor typically runs after a defrost cycle regardless of the compartment temperature. Such open loop defrost control systems, and the accompanying inefficiencies are undesirable in light of increasing energy efficiency requirements.
Recognizing the limitations of such timer-based defrost systems, efforts have been made to provide adaptive defrost systems employing limited feedback, such as door openings and compressor and evaporator conditions, for improved energy efficiency of defrost cycles. As such, unnecessary defrost cycles are avoided and the defrost heater is cycled on and only as necessary, such as until the evaporator reaches a fixed termination temperature. See, for example, U.S. Pat. No. 4,528,821. However, achieving some defrost goals, such as melting all of the frost off of the evaporator, are detrimental to achieving other defrost goals, such as maintaining freezer compartment temperatures at sufficient levels during defrost operations to prevent freezer burn and moisture formation/ice buildup in the freezer compartment. Known defrost systems have not resolved these difficulties in an energy efficient manner.